基于各向异性临界状态理论和考虑内结构影响的土体本构模拟

Any soil posses its specific fabric/internal structure. Upon loading, it often exhibits anisotropic mechanical behaviour. Mainstream constitutive models were established in the framework of isotropic critical state theory and failed to address the influence of the internal structure/fabric of the soils, thus leading to great uncertainties in their predictive performance. To overcome this, the common practice is to introduce certain empirical based mechanisms, which are largely phenomenological without any sound basis. In the light of newly established anisotropic critical state theory and new advances in this area, this proposal aims at describing the soil's complex anisotropic behaviour explicitly by integrating the variable of the internal structure with the yield functions. The dilatancy equations accounting for the influence of the internal structure can be obtained by laboratory element tests. A non-associative flow condition can be automatically satisfied when dilatancy relation is used to calculate the plastic volumetric strain increment. The hardening law can be established from the statistical analyses on the microstructure evolutions obtained from discrete element modeling. The proposed constitutive model is expected to simulate the soil response with varying initial conditions of soils under different loading stress paths. The model constants can be calibrated by conventional tests and the performance of the model will be verified by the experimental tests. The outcome of the proposed research will help to better understand the role of the internal structure plays in the mechanical behaviour of the soils and also will pave a way for the constitutive modelers to developing their sophisticated models.

任何土体都具有内结构而呈现各向异性的力学特性，建立在传统各向同性临界状态理论框架下的本构模型，由于未能考虑内结构的影响，往往导致预测不准确。为改善模型的预测性能，普遍做法是人为引入各种假定的唯象机制，所以具有较大的经验性和局限性。本项目拟基于最新的各向异性临界状态理论研究成果，在屈服函数中引入土体内结构的描述，显性模拟内结构影响下的土体复杂力学特性。采用试验手段获得描述考虑内结构影响的剪胀公式，用于计算体应变增量，以满足土体的体积非关联流动特性；通过代表单元离散元数值模拟，获得基于微观结构及其演化统计意义上的宏观硬化规律。建立的本构模型可以模拟不同初始条件和应力路径下土体的复杂力学特性，并依据试验结果对模型参数进行标定，验证模型的可靠性。通过本项目的实施，将为发展和完善土体本构模型提供有效途径，具有重要的理论价值和科学意义，也将为最终实现岩土工程问题的精细分析和科学设计提供可能。

本项目围绕提出的关键科学问题，从实验、数值模拟、本构关系等多个角度研究了土体各向异性内结构对其力学特性的影响。.通过开展针对各向异性砂土的静、动荷载试验，探究不同初始静剪条件下饱和砂土的单调与循环剪切行为及其内在关联，并考察动荷载不规则性对砂土液化特性的影响，进一步建立了能够考虑内结构演化和应力各向异性的砂土弹塑性本构模型。采用离散单元数值模拟，获得具有不同初始各向异性的试样，在三轴压缩和拉伸两种应力路径下进行数值模拟试验，并采用组构张量对砂土的各向异性进行量化，分析和探讨不同试样密度、围压、初始各向异性和、加载模式方式等及排水条件对砂土试样宏微观力学特性的影响，并对砂土临界破坏状态进行研究和分析，探讨临界状态线的唯一性。.以热力学原理为基础，建立了超固结土在不同固结应力路径下的本构模型，用于模拟不同固结应力历史的黏土剪切特性。基于各向异性临界状态理论，建立考虑组构演化和固结历史影响的各向异性本构模型，用来描述土体的复杂响应。基于各向异性临界状态理论，建立考虑组构演化和固结历史影响的各向异性本构模型，用来描述土体的复杂响应。针对砂土建立单剪切屈服模型，黏土则采用剪切与压缩双屈服面，并分别构建与不同屈服机制对应的流动法则和硬化法则。为了考虑固结历史对剪胀的影响，文中提出新的剪胀状态参数，较好地模拟各向异性固结土的剪胀与剪缩特性。该剪胀状态参数能够反映黏土超固结状态的影响，并较好地实现对于超固结土剪切与压缩特性的模拟。基于J2形变理论的状态相关本构模型。通过引入状态相关剪胀方程和修正应力应变关系的全量表达式，本模型能够解决形变理论和邓肯-张弹性模型的两个缺陷，用于有限元计算分析。基于各向异性临界状态理论，在亚塑性模型中引入用于反映土体内结构特征的组构张量，并定义表征各向异性的状态参数，通过该状态参数显式地反映组构及其演化对土体强度、剪胀特性的影响。建立的模型满足各向异性临界状态理论的要求。